Various skin replication methods have been used by researchers for years to study the external surface of the skin without the use of biopsies. These methods not only allow for the in vivo study of skin surfaces, but permit comparative observations to be made of topography of the skin prior to and after the application of various substances such as lotions, cosmetics, and medicinal mixtures.
Methods of studying skin surfaces by skin replication include the technique of making a negative impression of the skin surface at the test site and thereafter studying the negative impression or negative replica through the use of various types of magnifying equipment such as scanning electron microscopy (SEM). One method which uses this negative replica technique for studying skin surfaces involves the steps of placing a negative replica composition on the skin, curing the composition, removing the composition and studying the result by taking a picture of the negative replica while the replica is irradiated with light and observing the resultant pictures from the reverse direction.
Another method of studying skin surfaces entails the technique of making a negative replica of the skin surface test site and thereafter forming a positive replica from the negative casting. The positive replica is then evaluated through the use of some type of special magnifying equipment such as SEM. The methods and compositions used for forming the positive skin replica are varied. In one related art method, a negative replica of the test surface is made by covering the test surface with a silicone base material containing a catalyst and thereafter removing the polymerized replica. A mold held together by clamps is used to procure the positive replica. It is suggested that either polyethylene beads or a liquid cured Spurr imbedding resin be used to make the positive replica. Other methods of studying skin surfaces are disclosed in the references cited in applicant's Information Disclosure Statement.
While the related art methodologies appear to be effective in evaluation of skin surfaces, these methods have problems in that the compositions used to cast the negative replicas often prove to be an irritant to the subject's skin. Further, these methods often produce cracking of either the negative or positive replica and surface artifacts in the negative or positive replica caused by trapped air or by poor processing and selection of replicating materials. This cracking of either of the replicas and surface artifacts can introduce error in the researcher's results. Also, materials used to make the skin replicas in some related art methods produce a clear or white surface area which can present problems when attempting to visually evaluate and/or photograph such replicas. Additionally, in many instances in order to obtain accurate results, related art methods can only be performed with any degree of accuracy by technicians skilled in the art and with the use of special lab equipment. Further, the evaluation of the replicas must be done with special lighting or special diagnostic and magnifying equipment such as SEM, Image Analysis or Profilometry.